A radiation detector such as a conventional radiation detector to be used as a survey meter is for obtaining a dose rate as a dose per unit time and/or a counting rate as a count per unit time. In this case, first, a place where a natural radiation level (hereinafter, referred to as background) is significantly exceeded is found while moving, and next, at this place, measurement is performed for an appropriate period of time, and then a final dose rate or counting rate (also referred to as a final response value in a stationary state) is measured after stable indication is obtained in general.
Therefore, for example, in the case of an accidental radiation exposure emergency, to measure an air dose rate and/or a counting rate of a contaminated site, a wide range is measured while moving the radiation detector such as a survey meter, and at a place recognized as abnormal, the radiation detector is made stationary for measurement more than 30 seconds to 60 seconds, so that completion of the measurement consumes a great deal of time. When a measured value is read while the survey meter or the like is moved for inspecting contaminated sites, for example, when the distance to a measuring target is 10 mm, a time constant is 10 seconds, and a movement speed is 50 mm per second, an output suddenly lowers to about 10% to 15% of the final response value in a stationary state, so that it is difficult for unskilled persons to find abnormal sites under the present circumstances.
In the case of human body contamination inspection, when it takes a long time per one examinee, if a large number of examinees must be inspected, delay of the inspection and the exposure of the inspecting person become serious problems. Furthermore, routine radiation control takes a long time if the number of measuring sites is large.
On the other hand, a forecast responsive clinical thermometer which forecasts a final response value of a body temperature has been made practicable as one similar to the present invention. However, the number of electrons to be emitted from a thermistor or the like is large and the time constant is fixed and known, so that the forecasting is simple, and it cannot be used for a radiation detector in which emission of radiation occurs one by one as a probabilistic event and is greatly scattered.